
Hey there, Benjamin S
That's great you started learning for the exam, thanks for using QandA platform.
So I suggest you to start with the Microsoft learn platform where you can find self paced or instructor lead you will have two options and you can choose anyone and go ahead, as you were self-learning i recommend you to go through this, and it covers all the needed topics related to the ms900 exam,
also after this there are quite a lot of mocks available even a few are available in the same learn platform ill drop you the links below, All the very best for the examination. you got this,
https://learn.microsoft.com/en-us/credentials/certifications/exams/ms-900/
https://learn.microsoft.com/en-us/credentials/certifications/microsoft-365-fundamentals/
If this helps kindly accept the answer thanks much.